ABOUT the simplest staking operation to be found in watch work is staking the balance staff; that is to say, it is fundamentally simple; the conditions being correct, the riveting operation is of the very simplest character. Imperfect conditions is the stumbling block to many; the staff does not properly fit the hole; there is not enough stock projecting through the arm, to make a secure rivet; or, there is far too much; the part to be riveted is not sufficiently undercut, etc., etc.
Let us first consider the replacing of a balance staff, where we do not make the staff. The cases are rare where the part of the staff that goes in the balance should not be changed in some way; generally the riveting portion is too long. But let us first get the broken staff out without spoiling the balance arm. Do not, under any circumstances, drive the broken staff out without turning away the riveting so completely that the staff can be pushed out without distorting the balance arm or throwing the rim out of true in the slightest degree.
This is not for the reason that it would be difficult to true the balance, or anything of that sort, but because forcing the riveting through the hole tears away more or less of the comparatively soft metal of the arm, thus destroying the truth of the hole, and it also enlarges it by stretching the metal of the arm, making it oval or elliptic in form.
This makes it impossible for a new staff to fit properly, and is the beginning, generally, of a whole train of evils. Let us avoid all the trouble by turning away the riveting in the first place, as we should. There are several ways to do it, and whichever one we adopt, we must take due care not to turn away any of the balance arm.
Every watchmaker has discovered that American staffs are very hard to turn or cut with a graver. This is because they are made by a quite different process than the hand-made staffs. Factory-made staffs are turned out complete from the soft steel, then hardened and tempered; the requisite finish being given to the pivots, etc., afterward.
On the regular factory staff, absolutely no turning is done after the staff is hardened and tempered. This method of manufacture makes it possible, even desirable, to leave the temper of the staff harder than it is practical to make handmade staffs. When we say "practical" we mean just that. A staff can be turned as hard as a factory staff, but it isn't practical - takes too much time.
A few lines back we said it was desirable to have the staffs harder than hand-made ones. The reasons are: the pivots wear better; they are less easily bent. On the other hand, if bent, they are not so easy to straighten; but this, we think, can hardly be considered a disadvantage. A pivot once bent can never be as good as before, although it may serve, and in many cases, well enough.
For our own part we would prefer to have a pivot break square off before bending too much; it would be less likely to crack the jewel, and if bent very much, we wouldn't want to save it anyway, for the reason that it can never be restored to perfect form, without reducing it. The differences are not large enough to be shown on a foot rule, but they exist, and with proper instruments, can be clearly shown. To our mind the balance staffs which are driven in without riveting are a great step in advance; the idea is by no means new, but the originator arrived too soon; it took the world a great many years to catch up with him. With these staffs, a thousand could be inserted and removed from a balance with no injury to the balance, and practically no wear, for the walls of the hole are of tempered steel, and much greater surface than the regular kind.
True, a thousand staffs may be put in a regular balance, without injury, but it requires a higher grade of skill, and more time to do it; there's the point. Not that a high grade of skill is undesirable - far from it; but every unit of nerve force saved on the details of a job leaves the workman in just that much better form to apply the finishing touches to the job; the touches which count so much in the performance of the watch.
No smooth turning should be attempted; in fact, a graver sharpened on a rather coarse stone cuts these hard staffs more readily than one with a very smooth edge. It takes a good graver to cut these American staffs, but good gravers can be had, or easily made; anyway, never give up with less than actually cutting the staff away as we have indicated.
Well, assuming that we have removed the old staff, we must select a new one. The only dimensions we will concern ourselves with here is the part entering the balance arm; sometimes called the "waist," possibly because the arm encircles it. This part should fit the hole tightly enough to support the weight of the balance, when held up by the staff. It is a mistake to drive a staff very tightly into the arm; although it may go in somewhat more tightly than shown by the test we have mentioned; this is given to show what might be taken as a minimum. In any event the staff should not fit so tightly as to prevent it being inserted with the fingers, up to fully three-fourths the way to the shoulder. We should determine by measuring whether the bearing is of sufficient length to reach through the arm, and allow a sound riveting. This allowance for riveting will vary with different cases; depending somewhat on how much the hole in the balance arm is chamfered; but in no case should it exceed .1 mm., or about .004 inch; generally .002 inch is sufficient.
With a workman skillful with the graver, if the riveting allowance is too great, it may be cut down to the right length after the balance is pressed home on its seat. And in case we have to do this, it is well to cut the groove deeper than is usually done in factory staffs. Let the conditions resemble those shown in Fig. 3.
In the riveting operation, some prefer to turn the balance and staff slightly after each blow, rather than the punch, as we have directed; still others turn both; this a matter of personal preference, and equally good results may be had either way. It is better to change the relative angular position of the punch and staff, after each blow, however, no mistake about this, but just how it shall be done, each workman may decide for himself.
There is a class of cases, unfortunately too common, where the hole in the arm has been stretched, or at any rate, is slightly too large for the regular staffs; by "too large" we mean that the staffs would not be tight enough to meet the . requirements we have given as correct. Now, if the workman has to use such a staff, it is well to know how to rivet it with the least chance of the balance being found eccentric after the riveting is done. Mr. Bernard C. Husband, a skillful watchmaker, of Boston, inform the writer that most satisfactory results are secured in such cases by using the flat-faced punch first, in fact to do the entire riveting with the flat-faced punch.
In fine staffs, after riveting, we always like to touch up the undercut and riveting slightly, with very fine diamond powder, used on a piece of ivory, boxwood, or even pegwood; it gives it that crisp "better than ordinary" appearance, which we all like to give our work.